A relatively extensive series of neurophysiological studies on the hippocampus of the aging rat brain is proposed. Both in vivo and in vitro (hippocampal slice) preparations would be employed. The aged animals that would be used have been shown to exhibit a retention deficit that appears to be somewhat analogous to the deficit observed in aged humans. Differences between old and young animals would be investigated on a number of variables: potentiation, fatigue, conduction velocity, refractory periods, thresholds, spontaneous activity and excitability during disruption of inhibitory mechanisms. The several variables that differentiate old and young most consistently would subsequently be investigated in aged rats that had been carefully scored for degree of retention deficit on 2 tasks. The age-related neurophysiological change that was most highly correlated with the retention deficit in the same animals would be determined. Several pharmacological agents that have been reported to have beneficial effects on some of the symptoms of senility in humans would be studied in controlled conditions for their possible ability to reduce both the retention deficit and the correlated age-related neurophysiological changes. The primary goals of these studies are to investigate first, whether there are age-related changes in hippocampal physiology and, second, if there are, whether any of these are correlated with retention deficits; and third, can both the retention deficit and any physiological correlates of the deficit be reduced by certain pharmacological agents.